Plastic products are finding increasing application in automotive as well as consumer electronic markets. Since these products appear on the outside or exterior, their application demands good aesthetics not only in the initial stage of usage, but also during their continued usage. Plastics are known to get scratched quite easily or easily damaged from mar. To scratch means to break, mar, or mark a surface of by rubbing, scraping, or tearing with something sharp or rough. The surface of plastic parts can be visibly damaged in several ways, including (1) scratching by a sharp object; (2) abrasion by rubbing with an abrasive material or marring, which change the surface appearance or gloss; or (3) a “writing effect” of soft scratching with a dull object. A scratch is created when the material yields under an indentation, a sliding or lateral force, a ductile and/or brittle failure. In a scratch, an uneven surface results in non-uniform light scattering and “scratch whitening”. Solutions for improving scratch performance include minimizing roughness of the polymer ground and lowering the shoulder of the scratch, resulting in less light scattering and lower scratch visibility.
Not all polymers are easy to scratch but some are more sensitive than others. Polypropylene (PP), one of the fastest growing polymers in automotive interior applications, is one that gets scratched easily. This is a drawback as it is known that the aesthetics of an automobile's interior largely depends on the surface aspects of the plastic interior trim parts.
Several technologies have been used to deliver automotive interior surfaces which are scratch resistant and warm to the touch. For luxury vehicles, the plastic parts are coated with thermoplastic olefin (TPO) skins, fabrics or paints. This concept is out of price for less expensive cars. For these large consumption cars, a number of solutions have been proposed to improve the quality of interior plastics parts. These include the use of anti-scratch additives such as alkyl amides, for example erucamide or oleamide, that are capable of migrating during the injection-moulding of the parts to cover the surface (‘slip agents’) providing scratch resistance properties and a soft-touch feel of the parts. However, there exists a considerable gap in surface quality and robustness of slip agents compared to paints and coatings and the automotive industry is still looking for new solutions.
Siloxane masterbatches containing high molecular weight siloxane polymer dispersed in various thermoplastic resins have been successfully used in automotive interior and exterior components and in consumer applications such as laptop computers and cellular phone cases, and in tubing and film markets. The siloxane polymer migrates to the surface in the melt phase and gives scratch and mar resistance without the adverse effect of additive exudation of a small molecule additive.
Siloxane masterbatches are masterbatches containing siloxane. A masterbatch is typically a solid additive for plastic or other polymer which is used to impart desired properties to this plastic or other polymer. A masterbatch is typically a concentrated mixture of additives encapsulated into a carrier resin during a process involving heat, which is then cooled and cut into granular shape. This enables to impart desired properties to a polymer. Masterbatches are typically in solid form at ambient temperature, usually in pelletized format. Siloxane masterbatches are typically pelletized micro-dispersions of siloxane polymers, in various different plastic carrier resins at loadings of up to 50%. Siloxane Masterbatches are produced in solid form for ease of use. They typically contain 25-50% siloxane polymers (typically >15 million cSt) dispersed with for example an average particle size of 5 microns in various thermoplastics. A siloxane is a compound which contains at least one Si—O—Si link. A polymer is a compound containing repeating units. A plastic or organic thermoplastic material or thermoplastic organic polymer is a polymer based on C—C links and having thermoplastic properties. A siloxane polymer also called polysiloxane or silicone is a polymer containing repeating Si—O—Si units. An organopolysiloxane compound is a polysiloxane bearing substituents which constituents contain organic moieties.
The most commonly used silicones are linear PDMS (polydimethylsiloxanes) of various viscosities, ranging from the shortest possible chain, hexamethyldisiloxane with a viscosity of for example 0.65 cSt, to polymers with high degrees of polymerization and viscosities over for example 106 cSt, often called silicone gums. PDMS gums are usually fluids with viscosity around or higher than 600,000 cSt.
U.S. Pat. No. 5,844,031 describes a method of dispersing silicone compositions in organic thermoplastic materials. The compositions produced by the method of the invention have a fine and relatively uniform dispersion of organosilicone into the organic thermoplastic. An organosilicone resin (“resin” used herein to designate “MO” silicone resin) and a predominantly linear silicone fluid are first blended to substantial homogeneity to form an organosilicone alloy. The organic thermoplastic and the organosilicone alloy are thereafter mixed at predetermined mixing temperature and shear.
U.S. Pat. No. 7,838,581 discloses a polypropylene resin composition for interior materials of a vehicle comprising 30 to 70 weight % of an ethylene/propylene block copolymer, 10 to 30% of an ethylene/[alpha]-olefin copolymer rubber, 1 to 10% of a styrene-based polymer rubber, 2 to 8% of a polypropylene-silicone rubber master batch, 1 to 7% of a magnesium compound and 10 to 40% of an inorganic filler.
U.S. Pat. No. 6,602,953 discloses a polyoxymethylene resin composition for moulding applications containing silicone-grafted polyethylene to give good release and slidability, solvent resistance and thermal stability.
WO-A-2011/083044 describes a process for grafting silicone onto a polyolefin comprising reacting the polyolefin with a polyorganosiloxane in the presence of means capable of generating free radical sites in the polyolefin, wherein the polyorganosiloxane contains at least one unsaturated group of the formula —X—CH═CH—R″ in which X represents a divalent organic linkage having an electron withdrawing effect with respect to the —CH═CH— bond and/or containing an aromatic ring or a further olefinic double bond or acetylenic unsaturation, and R″ represents hydrogen or a group having an electron withdrawing effect with respect to the —CH═CH— bond.